Fluidic control circuits

ABSTRACT

The invention comprises a fluidic control circuit adapted to produce a high power output signal when the ratio of a first and second control pressure is above a predetermined value. The circuit includes a bistable coanda-effect device which changes its flow state in accordance with the said ratio. An output from the bistable device provides the control for modulating a relatively high pressure in an intermediate stage. The output of the intermediate stage forms a control for a final stage in which flow of fluid from a nozzle to an outlet is interrupted by causing swirling about the axis of the nozzle. Accurate sensing of pressure differentials by the bistable device is thus combined with the high power amplification of the output stage.

United States Patent 3,473,545 ill/i969 Boyadjiefi' ABSTRACT: The invention comprises a fluidic control circuit adapted to produce a high power output signal when the ratio of a first and second control pressure is above a predetermined value. The circuit includes a bistable coanda-elfect device which changes its flow state in accordance with the said ratio. An output from the bistable device provides the control for modulating a relatively high pressure in an intermediate stage. The output of the intermediate stage forms a control for a final stage in which flow of fluid from a nozzle to an outlet is interrupted by causing swirling about the axis of the nozzle. Accurate sensing of pressure differentials by the bistable device is thus combined with the high power amplification of the output stage.

PATENTfinJuualsn 3.592.209

sum 1 OF 2 INVENTOE W gg -"333 FLUlDlC CONTROL CIRCUITS This invention relates to fluidic control circuits and has an object to provide such a circuit in a convenient form.

A fluidic control circuit in accordance with the invention comprises a first stage constituted by a bistable coanda effect device with a first control port at which a first control pressure is applied and a second control port at which a reduced pressure derived from a second control pressure is derived and arranged so that the device changes flow state when said reduced pressure exceeds said first control pressure, an output stage in which flow of fluid from a nozzle to an outlet can be interrupted by causing swirling movement of the jet from the nozzle about the axis thereof, and an intermediate stage including a chamber the pressure in which is determined by the flow state of the bistable device and a pair of nozzles directed towards one another, one of said nozzles being connected to the output stage so that variations in the pressure in said one nozzle can cause said swirling movement of the jet therein and the other nozzle being connected to a fluid pressure source, the arrangement being such that the flow state of the bistable device will determine whether or not there is an output from the output stage.

Reference is now made to the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of one example of the invention,

FIG. 2 is a diagrammatic representation of a further exam ple of the invention, and

FIG. 3 is a diagrammatic representation of yet another example of the invention.

In each of the examples shown it is required to produce a high power output when a ratio of two pressures is above a certain predetermined value. A specific application in which the circuits are useful is the control of bleed valves for bleeding off part of the output of the compressor of a gas turbine engine. In this case the tappings are taken at an intermediate compressor position and at the compressor delivery, and the rise of the ratio of delivery and intermediate pressures above the predetermined value is required to signal closing of the bleed valves. in the following description P, is the compressor delivery pressure, P is the compressor intermediate pressure and P is atmospheric pressure.

in FIG. 1 the circuit has an input stage constituted by a bistable coanda effect device of known form. This device has a main inlet nozzle 11 receiving air at pressure P,, and two outlets l2, 13. The outlets have exhaust ports l4, 15 opening from them and there are a pair of control ports l6, l7 at the juncture of the diverging outlets. The arrangement is such that the admission of air into the device via the ports l6, l7 determines which of the outlets receives the air entering the device via the nozzle 11. If the pressure at port [6 exceeds that at port 17 the outlet flow will be via outlet 13 and outlet 12 will be at pressure P when the pressure at port 17 exceeds that at port 16 the outlet 12 will receive the flow and outlet 13 will be at pressure P,,.

Port 17 is connected to pressure P,. The port 16 is connected to a tapping in an air potentiometer constituted by restrictors l8 and 19 in series between the compressor delivery P and atmosphere P,,. Thus a reduced pressure derived from pressure P, is applied to port 16. Outlet 13 is connected via a restrictor 20 to drain.

The outlet 12 is connected to an intermediate stage 21 of the circuit. This stage 21 is constituted by a chamber which is connected both to the outlet 12 and, via a restrictor 22, to atmosphere P,,. Directed into the chamber 21 in opposite directions are a pair of aligned nozzles 23, 24. Nozzle 23 is connected to the compressor delivery tapping and nozzle 24 forms the output of the intermediate stage.

It is known that a device as described above operates so that under flow conditions the pressure in the nozzle 24 will differ from delivery pressure and is influenced by the pressure in the chamber 21. Moreover a given change in the chamber pressure will give rise to a substantially equal rise in the pressure in nozzle 24.

The output stage 25 of the circuit is constituted by a known vortex amplifier in which there is an inlet nozzle 26 aligned with an outlet 27 in a chamber 28 wit a dump port 29 connected to atmosphere. Normally a fluid delivered to the nozzle 26 is discharged from the outlet 27 without substantial loss. There is, however, a tangential control port 30 opening into chamber 28 such that introduction of pressure fluid into the chamber via this port will cause swirling of jet directed into the chamber about the axis of the jet. At a predetermined control pressure in the vicinity of the inlet nozzle pressure the swirling motion of the jet causes this to break up and the delivery ofpressure fluid from the outlet 27 ceases.

In the present case the nozzle 26 is connected to the compressor delivery P, via a restrictor 31. The control port 30 is connected to the nozzle 24. The components are chosen so that when the output of the bistable device is diverted to the outlet 12 thereof when the ratio P,/P, is below its set value the pressure applied to chamber 2] will be sufficient to raise the pressure in nozzle 24 high enough to create the swirling flow of the jet referred to so that there is no output from outlet 27. When pressure ratio PJP, rises above the set value and the bistable device changes its flow state the pressure in chamber 2l will fall so that the pressure in nozzle 24 will fall correspondingly and the swirling of the flow in chamber 28 will become insufficient to stop delivery of compressed air from the outlet 27.

In the case of the circuit shown in FIG. 2 the bistable device 10 and the output stage 25 are the same as before. The intermediate stage 32, however, is coupled to the bistable device 10 by an ejector 33 so that the pressure in the chamber of the intermediate stage 32 is held depressed when PJP, is below and rises to P, when P IP, is in excess of its set value. There is thus a corresponding rise in the pressure in nozzle 24 as before.

Turning finally to FIG. 3, there is a bistable device 10 and an intermediate stage 21 as in FIG. I, but the chamber 21 is connected to the outlet 13 instead of to the outlet 12. There is thus a rise in the pressure in nozzle 24 when P IP exceeds its set value.

The output stage 34 consists of a vortex device as described in our US. Pat. application Ser. No. 727,581. A chamber 40 contains a first nozzle 35 and an aligned second nozzle 36. Chamber 40 also includes a drain passage 41. The first nozzle 35 has a pair of inlets 37, 38, a chamber 42 and a nozzle outlet 43. inlet 37 communicates tangentially with chamber 42 so that fluid passing through inlet 37 tends to cause a swirling movement in one direction in chamber 42. Inlet 38 is also tangential to chamber 42 so as to tend to cause swirling in the opposite direction. The arrangement is such that if fluid is supplied to both inlets 37, 38 simultaneously, there will be created within the chamber 42 a fluid pressure which will be emitted as a stream through the outlet 43 in the direction of the second nozzle 36. If the pressures in the inlets 37, 38 are equal, there will be no tendency for the fluid in the chamber 42 to rotate about the axis of the nozzle 35 and accordingly, the emitted stream will be substantially cylindrical and lamina and substantial proportion of this will therefore be received in the nozzle 36.

If, however, the pressures in the inlets 37, 38 are unequal, there will be a tendency for the fluid to rotate inside the chamber 42 and it will thus be emitted as a substantially hollow cone of an angle such that there will be no appreciable recovery of the fluid in the nozzle 36.

ln the arrangement shown one inlet 37 is fed from the nozzle 24 and the other, 38, from a similar nozzle system 39, fed from the compressor delivery P,. The nozzle systems are balanced with the chamber 21 at P, so that the inlet pressures of the device 34 are equal. Thus, when P IP, is high and the output of the device 10 is from outlet 13 the pressure at inlet 37 will exceed that at inlet 38 and swirl will occur. Switching i' device when the ratio l lP falls below its set value will ause the pressure in chamber 2] to fall to P, thereby causing iressurized air to be delivered from the recovery nozzle 36 of he device 34.

In the case of the circuit shown in FIG. 3 an ejector like that hown in FIG. 2 could be employed so that the pressure in hamber 21 is reduced below P when P,/P, is above its set alue and rises to P, when an output is required from the evice 34.

In each of the above arrangements the accurate sensing of ressure differential obtainable from the bistable device is ombined wit the high power amplification ofthe output stage y the inclusion of the intermediate stage which allows moduition of a relatively high air pressure in the same range as the ressure to be applied as a result ofthe action ofthe circuit Having thus described my invention what i claim as new and esirc to secure by Letters Patent is:

l. A fluidic control circuit comprising a first stage con ituted by a bistable coanda effect device having an inlet, a air of outlets and a pair of control ports to which in use, a air of input signal pressures are respectively applied, so a ressure signal exists at a first one of said outlets when the itio of said input signal pressures exceeds a predetermined alue, an intermediate stage constituted by a chamber, means r causing the fluid pressure within the chamber to be depen' em on the pressure signal at said one outlet and a pair of anti lly aligned nozzles within the chamber, a fluid pressure ipply being connected, in use, to one ofthe nozzles, whereby ie fluid pressure in the other of the nozzles is dependent on ie pressure in said chamber, and an output stage constituted y a further chamber, an inlet nozzle within said further hamber and communicating, in use, with a fluid pressure ipply, an aligned outlet nozzle within said further chamber irming an output connection for the circuit and means for aplying to a fluid leaving said inlet nozzle of the output stage swirling movement whose magnitude is dependent on the ressure in said other nozzle of the intermediate stage, hereby the pressure at said circuit output connection is deendent on said ratio of the input signal pressures.

2. A circuit as claimed in claim 1 in which one of said input gnals comprises a first control pressure and the other of said .put signals is a reduced pressure derived from a second control pressure and in which fluid flows through said first outlet of the bistable device when the first control pressure exceeds the said reduced pressure, and through a second outlet of the bistable le device when the first control pressure is less than the reduced pressure.

3. A circuit as claimed in claim 2 in which the said first out let is connected to the chamber of the intermediate stage.

4, A circuit as claimed in claim 2 in which the said first outlet is connected to a pressure reducing means whereby the pressure in the chamber of the intermediate stage is depressed by fluid flow in the said first outlet.

5. A circuit as claimed in claim 2 in which the said second outlet is connected to the chamber of the intermediate stage.

6. A circuit as claimed in claim 2 in which the said second outlet is connected to a pressure reducing means whereby the pressure in the chamber of the intermediate stage is depressed by fluid flow in the said second outlet.

7, A circuit as claimed in claim 4 in which the pressure reducing means comprises an ejector devicev 8, A circuit as claimed in claim I in which the chamber of the intermediate stage includes a connection to exhaust via a restrictor.

9. A circuit as claimed in claim 1 in which the output stage comprises a vortex device which includes an inlet connected to the said fluid pressure source, a control port connected to the chamber of the intermediate stage, an outlet and a dump port.

it). A circuit as claimed in claim 1 in which the output stage comprises a vortex device which includes a first inlet supplied, in use, from the said fluid pressure source, an opposed second inlet connected to the chamber of the intermediate stage and an outlet. V I

ll. A circuit as claimed in claim 10 whlch includes a pair of axially aligned nozzles between the said fluid pressure source and the said first inlet.

I2. A circuit as claimed in claim 1 in which the said second control pressure forms the said fluid pressure source.

13. A circuit as claimed in claim 1 which includes a pair of restrictors connected in series, the said second control pot being connected to the junction ofthe said restrictors and the said second control pressure being applied to a side of one of the restrictors remote from the second control port. 

1. A fluidic control circuit comprising a first stage constituted by a bistable coanda effect device having an inlet, a pair of outlets and a pair of control ports to which in use, a pair of input signal pressures are respectively applied, so a pressure signal exists at a first one of said outlets when the ratio of said input signal pressures exceeds a predetermined value, an intermediate stage constituted by a chamber, means for causing the fluid pressure within the chamber to be dependent on the pressure signal at said one outlet and a pair of axially aligned nozzles within the chamber, a fluid pressure supply being connected, in use, to one of the nozzles, whereby the fluid pressure in the other of the nozzles is dependent on the pressure in said chamber, and an output stage constituted by a further chamber, an inlet nozzle within said further chamber and communicating, in use, with a fluid pressure supply, an aligned outlet nozzle within said further chamber forming an output connection for the circuit and means for applying to a fluid leaving said inlet nozzle of the output stage a swirling movement whose magnitude is dependent on the pressure in said other nozzle of the intermediate stage, whereby the pressure at said circuit output connection is dependent on said ratio of the input signal pressures.
 2. A circuit as claimed in claim 1 in which one of said input signals comprises a first control pressure and the other of said input signals is a reduced pressure derived from a second control pressure and in which fluid flows through said first outlet of the bistable device when the first control pressure exceeds the said reduced pressure, and through a second outlet of the bistable le device when the first control pressure is less than the reduced pressure.
 3. A circuit as claimed in claim 2 in which the said first outlet is connected to the chamber of the intermediate stage.
 4. A circuit as claimed in claim 2 in which the said first outlet is connected to a pressure reducing means whereby the pressure in the chamber of the intermediate stage is depressed by fluid flow in the said first outlet.
 5. A circuit as claimed in claim 2 in which the said second outlet is connected to the chamber of the intermediate stage.
 6. A circuit as claimed in claim 2 in which the said second outlet is connected to a pressure reducing means whereby the pressure in the chamber of the intermediate stage is depressed by fluid flow in the said second outlet.
 7. A circuit as claimed in claim 4 in which the pressure reducing means comprises an ejector device.
 8. A circuit as claimed in claim 1 in which the chamber of the intermediate stage includes a connection to exhaust via a restrictor.
 9. A circuit as claimed in claim 1 in which the output stage comprises a vortex device which includes an inlet connected to the said fluid pressure source, a control port connected to the chamber of the intermediate stage, an outlet and a dump port.
 10. A circuit as claimed in claim 1 in which the output stage comprises a vortex device which includes a first inlet supplied, in use, from the said fluid pressure source, an opposed second inlet connected to the chamber of the intermediate stage and an outlet.
 11. A circuit as claimed in claim 10 which includes a pair of axially aligned nozzles between the said fluid pressure source and the said first inlet.
 12. A circuit as claimed in claim 1 in which the said second control pressure forms the said fluid pressure source.
 13. A circuit as claimed in claim 1 which includes a pair of restrictors connected in series, the said second control pot being connected to the junction of the said restrictors and the said second control pressure being applied to a side of one of the restrictors remote from the second control port. 